1. Field of the Invention
This invention relates to pneumatic radial tires having improved running performances.
2. Related Art Statement
Particularly, the improvement of the running performance in this type of the tire is strongly demanded in pneumatic radial tires for passenger cars because it is required to always ensure a stable steering property in the passenger car in accordance with remarkable fullness of the equipment and performance in the passenger car as well as the enlargement and development of road networks
In order to improve the running performance of the pneumatic tire, it is necessary to have sufficient rigidity in the tread portion and bead portion of the tire. For this purpose, there is considered a countermeasure of strengthening the reinforcement at the tread and bead portions, a countermeasure of raising an air pressure filled in the inside of the tire, and the like.
However, the quantity of reinforcing member required and used for strengthening of the reinforcement is generally increased to undesirably raise the cost. On the other hand, as the internal pressure becomes higher, the ground contact area of the tread portion reduces to obstruct the transmission of necessary force, and consequently the steering performance, and traction and braking performances are degraded.
That is, the tire should be used under such an internal pressure as to hold a balance capable of accepting merits through the strengthening of the rigidity and demerits due to the degradation of the performances. However, the strengthening of the rigidity without causing the increase of the cost can not be achieved by the above conventional technique.